1. Field of the Invention
The present invention relates to a method for recovering nickel from an sulfuric acid aqueous solution, and more specifically the present invention relates to a recovering method for nickel from the sulfuric acid aqueous solution, which is capable of enhancing economical efficiency as a smelting process, as well as recovering nickel in an effectively utilizable form as a raw material of nickel industry material such as metallic nickel, nickel oxide, ferronickel, and at the same time, separating cobalt, which is an expensive valuable metal, as a byproduct easy to utilize, by removing efficiently impurity elements of iron, aluminum, manganese and the like, from the sulfuric acid aqueous solution containing nickel and cobalt, and the impurity elements of iron, aluminum, manganese and the like. In this way, the present invention is suitably used as a method for separating and recovering nickel and cobalt from a leach solution containing various kinds of impurity elements produced from the leaching step of various leach methods such as a High Pressure Acid Leach Method for a nickel laterite ore.
2. Description of the Prior Art
Conventionally, there has been required technology to separate and recover nickel economically efficiently from the sulfuric acid aqueous solution containing nickel, along with the impurity elements of beginning from cobalt and other various kinds. For example, in recent years, in nickel smelting process, a hydrometallurgical process has been attracted attention, which is based on an acid leach method of a nickel laterite ore with a sulfuric acid solution. This acid leach method does not include the dry step such as the reducing step, the drying step, differing from a pyrometallurgical process, which is a conventional general metallurgical process for a nickel laterite ore, and is thus advantageous in view of energy cost, therefore, it is viewed as promising technology as a metallurgical process for a low content nickel laterite ore, for example, having a nickel content of about 1 to 2% by mass, also from now on. In such a hydrometallurgical process, a leach solution to be produced is the sulfuric acid aqueous solution containing nickel, along with various kinds of impurity elements such as, beginning fromcobalt, iron, aluminum, manganese, zinc, chromium, magnesium, silicon, contained in an ore, and it was an important problem in view of a smelting process, to separate and recover nickel, and cobalt, if necessary, by an efficient means.
It should be noted that, as the above hydrometallurgical process, for example, the following processes (A) to (C) have been proposed.
Hydrometallurgical Process (A):
This method is composed of the following steps (1) to (4), and produces mixed sulfides containing nickel and cobalt from a nickel laterite ore, using a High Pressure Acid Leach Method (for example, refer to Patent Document 1).    (1) Leaching step: to make slurry of a nickel laterite ore and to add sulfuric acid, and to stir at a temperature of 220 to 280° C., to form leaching slurry.    (2) Solid-liquid separation step: to wash the aforesaid leaching slurry using a thickener with multi-stages to separate it into a leach solution containing nickel and cobalt, and a leach residue containing iron as hematite.    (3) Neutralization step: to adjust pH to equal to or lower than 4 using calcium carbonate, while suppressing oxidation of the aforesaid leach solution to generate a neutralization precipitate containing trivalent iron and to separate it into neutralization precipitate slurry and mother liquor for nickel recovery. and    (4) Sulfurization step: to blow hydrogen sulfide gas into the aforesaid mother liquor for nickel recovery to generate a sulfide containing nickel and cobalt, and to separate it from barren liquor.Hydrometallurgical Process (B):
This method is composed of the step to form a leach residue by converting iron to natrojarosite, and obtain a leach solution containing nickel and cobalt; the step to remove iron and aluminum by adding a neutralizing agent to the resultant leach solution; the step to obtain a extraction residual liquid containing nickel and a back extraction liquid containing cobalt, by solvent extraction treatment of the resultant neutralized solution with a monothiophosphinic acid compound as an extraction agent to extract cobalt; and the step to obtain a hydroxide by neutralizing the resultant extraction residual liquid containing nickel and the back extraction liquid containing cobalt, with an alkali, respectively, in leaching by adding sulfuric acid to a nickel laterite ore. Subsequent to these steps, still more, after removing sulfur and chlorine by washing the resultant nickel hydroxide with an alkali solution, by supplying it, with the nickel laterite ore, to a ferronickel production plant including firing and reduction melting steps, nickel hydroxide is used as apart of raw materials for ferronickel production (for example, refer to Patent Document 2).
Hydrometallurgical Process (C):
This method is composed of the step to obtain an acidic eluent containing nickel with a Ni concentration of 10 to 80 g/L, cobalt, aluminum, iron or the like, by separating a resin, which absorbed nickel and cobalt, from slurry, and leaching this resin; the step to remove iron and aluminum by neutralizing the aforesaid acidic eluent at a pH of 4.5 to 5; the step to obtain an extraction residual liquid containing nickel and a back extraction liquid containing cobalt, by solvent extraction treatment the resultant neutralized solution with an extraction agent, Cyanex 272, to extract cobalt, manganese or the like; and the step to obtain a hydroxide by neutralizing the resultant extraction residual liquid containing nickel with magnesium hydroxide; in what is called a RIP (Resin In Pulp) method, in which an ion-exchange resin is added into acid leach solution slurry of a nickel laterite ore formed in the atmospheric pressure step or the high pressure acid leaching step (for example, refer to Patent Document 3).
However, in the hydrometallurgical process (A), because it is one not to separate nickel and cobalt, and recover them as mixed sulfides, although the resultant mixed sulfides are suitable as raw materials of a smelting process provided with the steps to leach them, then separate nickel and cobalt to recover each of them as a highly pure product, for example, a chlorine leach method, but on the other hand, it had a problem not able to be used directly, as raw materials for production of, for example, ferronickel or stainless steel production, in a process having limitation in view of load of cobalt, sulfur or the like in supplied raw materials.
In addition, in the hydrometallurgical process (B), although the resultant nickel hydroxide can be used as a raw material of ferronickel production, because cobalt has been separated and sulfur has been removed, but on the other hand, there was a problem, as a problem in view of a smelting process, that nickel concentration of a neutralization solution, as a starting solution of the solvent extraction step, is several g/L, the same level as that of a leach solution, because the special step is not installed for increasing nickel concentration of the leach solution and the neutralization solution, and thus in a solvent extraction treatment using such a low concentration solution, use amount of the extraction agent and equipment scale become too large, which is not economically efficient due to loss of the extraction agent and equipment cost.
In addition, in the hydrometallurgical process (C), although the resultant nickel hydroxide, in which cobalt is separated, and thus can be utilized effectively as a raw material of metallic nickel, nickel oxide, ferronickel or the like, but on the other hand, there was an economical problem in a leach method itself, because the RIP (Resin In Pulp) method is adopted in the leaching step, as a smelting process, because of wear or the like of an expensive ion-exchange resin in slurry, use amount and loss thereof becomes excessive, as well as nickel concentration of an acidic eluent, as a starting solution of the solvent extraction step, is 10 to 80 g/L at most, although concentration effect is expected by use of the ion-exchange resin, and thus in a solvent extraction treatment using such a low concentration solution, use amount of the extraction agent and equipment scale become excessive, similarly as in the hydrometallurgical process (B).
In addition, in the hydrometallurgical processes (B) and (C), because the special step is not installed for removing manganese from the starting solution of the solvent extraction step, in adopting a phosphate ester-type acidic extraction agent as the extraction agent to extract cobalt from the starting solution to an organic phase, extraction efficiency of cobalt deteriorates influenced by manganese extracted together, therefore, there were also problems of increase in use amount of the extraction agent and increase in manganese concentration in the back extraction liquid containing cobalt.
In view of the above circumstances, there has been required a method which is capable of enhancing economical efficiency as a metallurgical process, as well as recovering nickel in an effectively utilizable form as a raw material of nickel industry material such as metallic nickel, nickel oxide, ferronickel or the like, and at the same time, separating cobalt as a byproduct easy to utilize, by removing efficiently impurity elements of iron, aluminum, manganese and the like, from the sulfuric acid aqueous solution containing nickel and cobalt, and the impurity elements, iron, aluminum, manganese and the like.